Internal combustion engine crankcase ventilation is generally understood to be required to remove combustion gases and unburned hydrocarbons, termed "blow-by gases," that leak by piston rings during combustion, leading to degradation in engine component materials and contamination of engine oil. Positive crankcase ventilation (PCV), purges blow-by gases from the engine crankcase, separates oil from the blow-by gases and returns the gases to an engine intake manifold to be consumed. PCV systems typically are relatively complex, including a purge control valve (PCV valve) and a plurality of flow lines with connections between the crankcase, the intake manifold, and a fresh air source. Flow restrictions in the PCV valve or in any of the flow lines, or leaks in the flow lines can interfere with effective purging of the blow-by gases, potentially leading to reduced engine performance and increased emissions. Currently, only when such restrictions or leaks are of an extreme character, for example as may cause perceptible degradation in engine performance, are they diagnosed and eventually treated. A performance or emissions penalty may be paid from the time the restriction of leak condition develops to the time of proper treatment thereof.
Copending U.S. patent application Ser. No. 08/705,895, filed Aug. 28, 1996, U.S. Pat. No. 5,792,949 assigned to the assignee of this application, discloses diagnosing a PCV system by monitoring PCV system pressure during a stable engine operating condition. Pressure excursions outside a pressure range are diagnosed as a leak or a restriction condition in the PCV system and are indicated. PCV system pressure monitoring requires exposure of pressure transducers to high contaminant levels and substantial temperature variation in the PCV system, which may reduce transducer life or increase transducer cost. Further, such prior art diagnostic may be engine crankcase volume (and therefore engine application) sensitive, leading to significant calibration effort to transport the diagnostic between engine applications.
Copending U.S. patent application Ser. No. 08/740,177, filed on the filing date of this application, attorney docket number H-197597, assigned to the assignee of this application, discloses diagnosing a PCV system by varying a restriction to flow through the PCV system and through synchronized sampling of engine intake mass airflow rate. If the sampled air rate changes in a manner significantly different than that expected for the controlled change in PCV system airflow restriction, a fault condition may be indicated. Such diagnostic requires an additional actuator which may be controlled in a manner intrusive upon other control operations and requires relatively complex synchronized parameter sampling to measure the impact of the varied PCV system flow on engine intake mass airflow rate. System cost and performance may be compromised under such approach.
Accordingly, it would be desirable to provide for low cost, simple, non-intrusive diagnosis of a PCV system which may easily be applied over a range of engine applications.